Grendel not optimal for AR-15-sized magazines?

[SOFShooter]

I just got done playing with the latest iteration of trying to find functioning magazines (both hi-cap & mid-cap).
I ordered 2 PRI 6.8 magazines, 26 rd and 10 rd, and neither will work with more than 5 rounds each; the usual nose dive and sticking on feeding and swelling of mag bodies to the point where they will not insert.
I have played with USGI mags, C-products mags, ASC mags and now PRI mags and I have the following hypothisis:
The 6.8 SPC cartridge is the largest diameter cartridge that will give a true double stack in a AR-15 sized magazine (the same size mag bodies as our Grendel mag bodies (shallow ribs)).
The Grendel cartridge is too large in diameter to allow a correct double stack in an AR-15 sized magazine. What we get is a zig-zag stack with rounds on the same side not in proper contact with the rounds above and below. As more rounds are loaded, the more side pressure is placed on the magazine body, causing swelling, and higher friction due to pressure between rounds (think 2 cylinders trying to pass each other in a space slightly less than double the diameter of the cylinders).
This is why, in my opinion, 6.5 Grendel magazines will always be marginal in the AR-15, just like 7.62 X 39 mags: Some people have glowing results and some don't, so many have posted that 3 or 4 in a mag is OK, but no more than that, etc.
I think we need a good single-stack magazine design that will fit in the AR-15 magwell (and possibly open up into a proper double stack design below the magwell).
Otherwise, we need a special lower with a wider magwell and wider magazines to match, giving a proper double-stack to our cartridges.
I look foward to this discussion.
SOFShooter

[Bill Alexander]

You must be unlucky!

The ASC Grendel magazines seem to run superbly. Given a specification magazine well, a correct double stack magazine allow for 0.035" wall thickness with adequate space for the magazine to drop free. The design does preclude a polymer side wall as it is rater thin but for a metallic magazine, not impossible.

The rounds stack correctly with contact between rounds in each column. This allows for the correct feeding and the guns run well both in semi and full auto.

While ASC is not the original supplier, the magazines are in essence the same design we originated for the Grendel, together with the follower we designed. If you try and use either 5.56 magazines or incorrect followers the stack can become unordered either at the rounds on the follower or throughout the stack depending upon the problem. In all cases the round will not feed well or the follower will bind.

D&H are currently completing design work on Grendel magazines and we should see this option soon.

[Bill Alexander]

Just read a few other posts, are you fire forming brass? Some brands of 7.62x39 will have a slightly greater base diameter. Nominal is set at 0.438" at the case web. I have seen soft fire formed stuff go as large as 0.450"

[stanc]

I just got done playing with the latest iteration of trying to find functioning magazines (both hi-cap & mid-cap).
I ordered 2 PRI 6.8 magazines, 26 rd and 10 rd, and neither will work with more than 5 rounds each; the usual nose dive and sticking on feeding and swelling of mag bodies to the point where they will not insert.
I have played with USGI mags, C-products mags, ASC mags and now PRI mags and I have the following hypothisis:
The 6.8 SPC cartridge is the largest diameter cartridge that will give a true double stack in a AR-15 sized magazine (the same size mag bodies as our Grendel mag bodies (shallow ribs)).

Hmm. My first reaction is to wonder if you are a 6.8 fan trying to foment discord in the horde.

It seems unsurprising to me that magazines made for 5.56 and 6.8 do not work well with 6.5 Grendel, due to the different cartridge geometries.

The Grendel cartridge is too large in diameter to allow a correct double stack in an AR-15 sized magazine. What we get is a zig-zag stack with rounds on the same side not in proper contact with the rounds above and below.

Have you actually cut away Grendel mags to see that rounds are not stacking properly, or are you just assuming they don't?

This is why, in my opinion, 6.5 Grendel magazines will always be marginal in the AR-15, just like 7.62 X 39 mags: Some people have glowing results and some don't, so many have posted that 3 or 4 in a mag is OK, but no more than that, etc.

If your hypothesis were correct, shouldn't everybody have problems? Might the inconsistency be better explained by inadequate control over manufacturing tolerances?

I don't know if 6.5 Grendel is too fat for proper stacking in the current magazine design, but it is interesting to note that the original 17-round mags (marketed by AA back in 2005) did not have a rear reinforcing rib, thereby maximizing internal width.

[SOFShooter]

Thanks, Bill!!!!

I AM fireforming Winchester 7.62 X 39, web diameters of .440"+, RIM diameters of .443"-.445"!!!
The cases are what I started with and have a bunch of, so I haven't tried anything else!
I have 2 boxes of Wolf 120 MPT that I have never fired and the web is .438" +/- and rim is .438"-.439".
I'm gonna play with the Wolf now and see if it looks better.
Remember, in today's climate, one is never "unlucky", one is a "victim" (in my case, of tolerance stacking maybe).

SOFShooter

[RangerRick]

You must be unlucky!

The ASC Grendel magazines seem to run superbly. Given a specification magazine well, a correct double stack magazine allow for 0.035" wall thickness with adequate space for the magazine to drop free. The design does preclude a polymer side wall as it is rater thin but for a metallic magazine, not impossible.

The rounds stack correctly with contact between rounds in each column. This allows for the correct feeding and the guns run well both in semi and full auto.

While ASC is not the original supplier, the magazines are in essence the same design we originated for the Grendel, together with the follower we designed. If you try and use either 5.56 magazines or incorrect followers the stack can become unordered either at the rounds on the follower or throughout the stack depending upon the problem. In all cases the round will not feed well or the follower will bind.

D&H are currently completing design work on Grendel magazines and we should see this option soon.

+1 on that. I have ASC mags and C-Products. I have zero problems with the 25 and 10 round mags. The 17 rounders only hold about 14.

I shoot Lapua, Hornady, and IMI 7.62x39 fire formed brass. All feed fine.

Great news on D&H Bill. I've been hearing rumors about this. Looking forward to trying some.

RR

[SOFShooter]

I just tried my factory Wolf 120 MPT rounds in my c-products, ASC & PRI 6.8 mags: same thing, these mags, for whatever reason are not "double stacking" correctly (and no, you don't have to cut them apart to see it).
Just three rounds in, you can see the zigzag (space between the 1st and 3rd round on the left side by looking down the bolt lock channel, more rounds down, you can see the gap on the left side by looking in the mag catch cutout.
I don't own a 6.8, but I have many 6.8 rounds in my little collection that I have picked up over time and these rounds double stack nicely in the above magazines (who knows if they feed or not).
I would be interested to see pics of 6.5 Grendel stacked up in various magazines, especially at the top rear of the mag and mag catch hole (with enough rounds in it, of course).
I look forward to the D&H mags, soon I will have collected the entire series ; )
By the way, as a test, I have used graphite generously in the c-products mag (dusted on the rounds as you load just as you would for a .223 Beta c-mag) and had that mag full actually feed completely; as soon as the graphite is wiped out, back to jam city.

[seatleroadwr]

I'd like to see a magazine that will accept a cartridge with a COL of 2.300. The PRI mag does this with room to spare but it has feeding problems.

[SOFShooter]

"The 17 rounders only hold about 14."
I locked up on this statement. Do these mags actually bottom out the follower and spring at 14 rounds, or, at 14 rounds, does adding additional rounds start to swell the mag or become so hard to load due to friction that additional rounds won't function? And why just on the 17 round mags if they are the same body and follower as 10's or 25's?

SOFShooter

[LRRPF52]

SOFShooter,

Are you using 6.8 mags for the Grendel? The 6.8 has a narrower case head diameter, so it would make sense if they have deeper guide grooves down the side, whereas the Grendel's are very shallow, unlike a 5.56 mag.

I have also been thinking that I needed to get some 6.8 mags so I could load to 2.300" COAL, but then I went and double-checked my 10rd, 4rd, 17rd, and 25rd CPRoducts Grendel mags, and lo and behold, I can load to 2.305" if I find pills that will chamber that long.

[Bill Alexander]

it is not likely that the Grendel will stack correctly in 6.8 magazines. The internal width has to reflect the cartridge diameter, as does the cartridge shelf on the follower.

One of the problems we encountered with the Grendel is that the magazines have to be correctly manufactured, to print, or the stack will not work. The original CProducts magazines would suffer from production variations. In our operation we would always unpack each magazine and then check all the critical dimensions before we would ship to customers. The magazine body is stainless and they are heat treated once welded. If the baskets are packed too tight the mags would deform and not feed. It is heart breaking to simply send back a pallet of mags when everyone is screaming for product but we have been there. Ribs must be correctly formed to allow the units to feed. One of the criticisms we always got was, why are our mags more expensive, when they are just CP with a different floor plate.

Fast forward to the new ASC and we are lucky to have the same engineers as before but with better QC. Despite this we hit several initial teething problems with the early deliveries. One of the temptations for the producers is to try and commonize stuff like the followers, which will not work.

I know PRI well and have even looked at the mags they make. Mr Dunlap who runs/owns the business is a gentleman and I would recommend their scope rings to anybody. (they make great hand guards as well). We both concluded that the material they use is a little heavy and that a new design would be required to feed the Grendel reliably.

The new CProducts Defence does not make a Grendel magazine.

So to sum up The Grendel will work reliably as intended, but you have to have the correct magazines and they have to be correctly manufactured.

And this brings us to the 17 round debacle. These magazines were originally intended to be formed from the 25 round bodies and would incorporate some curvature. Fashion and a sales manager saw fit to make a straight body instead and the rounds will overtake the body. The only redeeming feature has been extended legs on the follower restrict the capacity well below the intended so the FU is not too bad. Alexander Arms does not use or sell these magazines.

[Bill Alexander]

I am intrigued by this sudden rush to make ammunition that is too long to feed reliably in the weapon. If you have a piss poor Bc then grabbing length in front of the case mouth for a longer ogive makes some sense, but the Grendel does not suffer from this. Equally our chamber, more particularly the throating is balanced as best we can to be able to accept and shoot most projectiles when loaded and shot from the magazine.

For reference, the % increase in velocity is usually close to 1/4 of the % volume increase. AI cases rarely see much difference, but the proponents do not tend to calibrate the pressures and enthusiastic hand loading to support ones pet project seems to prevail. Extended lengths make even less sense as the volume added is insignificant when converted to a velocity gain.

I will endeavor to take some photographs of loaded magazines.

Finally I know that a wider receiver is now all the rage but the essence of the work is compatibility with the AR platform. While width is not as detrimental to the weight spiral as extending the weapons action length, anything that increases the weapons size envelope will negatively effect weight.

[Drifter]

The new CProducts Defence does not make a Grendel magazine.

It appears that CPD offers Grendel mags:

http://www.cproductsdefense.com/Products/Products.html

In stock at:

http://lcjwholesalestore.com/

http://shop.lcjwholesalestore.com/searchquick-submit.sc?keywords=grendel

[Bill Alexander]

CProducts Defense does not make Grendel magazine! It is a 6.8 done badly.

[SOFShooter]

Thanks, Bill!!! It looks like I will be ordering 2 magazines from you tomorrow (10rd, 25rd)!!!

My magazines all appear to be out of spec. and are not stacking anywhere near correctly. (NOT the PRI 6.8 mags - they are a different animal I am learning)

This forum (and I, as a member) need to quash (by way of polite replies) all threads or replies recommending 6.8 magazines as a possible fix for feeding problems. At best they are in the category of "a few rounds will work", just like 5.56 GI mags, P-mags, etc.

SOFShooter